With development of metallurgic technology in the world, modern continuous casting technology makes progress, the varieties of castable steel are increasing and some steel varieties with high alloy, high quality and high cracking susceptibility have been put into production in continuous casting production process in large-scale steel enterprises. Among them, one of the important technical progresses is development and application of chamfered mould technology.
Especially, the development of large-section slab continuous casting technology increases the compression rate of the steel materials and enhances the quality of the steel materials. But expansion of the slab section brings out an adverse influence: slab needs to be bent and straightened in casters so the cracks on angles of the slab may be increased. Specially in recent years, the thickness of the slab for large slab continuous caster has reached and even exceeded 250-450 mm, the thickness of large square and rectangle slabs even exceeds 350-500 mm. Due to uneven cooling of the angle, the stress will definitely cause the increase of the slab corner crack during the bending and straightening process.
Therefore, besides optimization in molten steel equality and second cooling technology, one of the major technical measures taken by metallurgic engineers is adopting chamfered mould technology which changes two existing right angles of the slabs into two obtuse angles (chamfered) so as to eliminate the stress.
The mould technology with chamfered side plates is common in prior arts. Generally the narrow side copper plate for mould with chamfered sides in two forms: one is a separated chamfer which is grasped between the narrow side and wide side of the mould; another is integrated as one which is respectively provided at left and right sides of the narrow surface copper plate for mould.
The separated chamfer between the wide side copper plate and narrow side copper is cooled by means of contact, so the chamfer is provide in small size, generally in 3-10 mm. The chamfer angle is 45° and is equal from top to bottom on any cross section, thus the service life is short.
Chinese utility model ZL 02214026.3 (Publication No.: CN2547438Y, titled “A narrow side copper plate for slab continuous casting mould”) provided a kind of the narrow side copper plate for mould with chamfered sides, which chamfer is 45° with size of 6-10 mm. The chamfer angle is 45° on any cross section, but fails to point out the contraction of the narrow side copper plate from top to bottom in the width direction.
Chinese utility model ZL 200720089029.7 (titled “A kind of slab mould”) provides a kind of chamfered narrow side copper plate with an arc transition surface for mould. Similarly, this patent fails to point out the change of chamfer of the narrow side copper plate from top to bottom. A conclusion can be drawn through analysis of this patent: the curve shape and size of the chamfer are unchanged from top to bottom.
In practical production, the narrow side of the mould has a taper. A Chinese literature “Mould Cross-sectional Dimension & Taper Design” (source: Cheng Zhigang. CFHI Technology, Volume 3, 2008, p 30-31) analyze the use of the taper of the mould and points out that, the taper of the mould is 0.6%-1.1% generally. In practices, the taper at the narrow side of the mould for traditional large slab continuous caster is within 1-1.5 mm generally. The narrow side copper plates for mould are grasped between the wide side copper plates for mould, so the taper of the narrow side is realized by making the big width on top and small width on bottom. For instance the width on top of the narrow side copper plate is 1 mm longer than the bottom.
Some chamfered narrow side of mould also show a taper which is realized by the big width on top and small width on bottom of the middle plane area of chamfered narrow side copper plate for mould. So far there is no literature or report about the taper of the chamfered narrow side copper plate for mould.
It can be realized from aforementioned cases that all of moulds for traditional continuous casting have the taper with the big width on top and small width on bottom. The technology of the narrow side copper plate for mould with chamfered sides has been used in practices for many years, the chamfered surfaces are plane forms and various different curved surfaces. However, the taper of the bevel of the chamfer has not been considered in existing chamfered mould technologies. Especially when the chamfer is large, e.g. larger than 30 mm, the ignorance of the contraction during solidification will definitely cause the poor cooling effect of the chamfer and cracks occurring on the shell in the mould. That has become an important challenge for application of the narrow side copper plate for mould with large chamfered sides in the production of slab and bloom.
Aiming at the above defects and deficiencies, this invention provides one chamfered narrow side copper plate for mould with funnel-shaped curved surface.